In the wee hours of the morning a few days before Thanksgiving, 2000, when Dick Cheney showed up in the George Washington University Hospital emergency room complaining of chest discomfort, he received nothing more than standard medical care. That standard care is likely to have saved him from experiencing a full-blown myocardial infarction (heart attack), or even death, in the relatively near future. Without that care he may never have gone hunting again.
Hundreds of thousands of Americans each year have the same problem Mr. Cheney experienced that morning – unstable angina. Unfortunately, many of them receive something less than the standard of therapy received by Mr. Cheney.
In this article we will review unstable angina – what causes it, how it differs from a classic heart attack, how it is diagnosed, and how it ought to be treated.
Unstable angina? Those of us old enough to remember will recall that the papers claimed Mr. Cheney had a heart attack, not unstable angina. And strictly speaking, he did.
But the amount of heart muscle damage he experienced was so tiny that it would have been undetectable just a few years ago. As recently as the mid-1990s, it is likely Mr. Cheney would have been sent home from most emergency rooms with the diagnosis of a “simple angina,” or even “chest pain of non-cardiac origin.” And until a few months ago, even with the correct diagnosis, it is likely he would have been managed much more conservatively, with outpatient drug therapy only.
What has changed? Two things: our understanding of the cause of unstable angina, and our understanding of the best way of diagnosing and treating it.
What is unstable angina?
Stable angina, unstable angina and myocardial infarctions ultimately are all caused by the same process – coronary artery disease.A myocardial infarction, or heart attack, occurs when a plaque ruptures in a coronary artery, leading to the sudden formation of a blood clot superimposed on the plaque. The blood clot often totally occludes the artery, leading to death of the heart muscle being supplied by that artery. And a myocardial infarction is the death of heart muscle.
Unstable angina occurs when a blood clot forms on a plaque, suddenly increasing the degree of blockage in a coronary artery. By definition, in unstable angina the clot does not completely occlude the artery, but merely increases the degree of blockage. Because blood flow across the blockage suddenly becomes more sluggish, angina occurs even at rest.
Indeed, the blood flow can become so sluggish, and the angina can persist for so long, that some of the heart muscle cells being supplied by the partially occluded artery can actually die in patients with unstable angina. Since the death of heart cells is the definition of a myocardial infarction, once some of the cells die, the patient has “officially” had a heart attack. Click here for a pictorial explanation of how the blood clots, and how a blood clot can produce unstable angina.
Our ability to detect cell death in patients with unstable angina has greatly improved over the past few years, mainly by the development of more sensitive assays for the enzyme, troponin. Troponin is a heart muscle protein that is released into the bloodstream when heart muscle cell death occurs. As our ability to measure troponin increases, more and more patients with unstable angina are being diagnosed with heart attacks.
This is what happened in Mr. Cheney’s case. His troponin level was found to be elevated a few hours after he was admitted, and this tipped off his doctors that his coronary artery blockage was severe enough to be causing cell death – albeit a very tiny amount of cell death.
